Rubber thread

ABSTRACT

A rubber thread includes in cross-section a first rubber portion and a second rubber portion.

This is a divisional of application Ser. No. 08/540,180 filed Oct. 5,1995, now 5,679,196.

BACKGROUND OF THE INVENTION

The invention relates to rubber thread.

Rubber thread is commonly used in a number of products, including narrowelasticized fabric for textile applications such as waist bands andshoulder straps of foundation garments, for toys, and for braided("bungee") cord. Rubber thread typically is composed of natural rubber,which has excellent resiliency and other desirable properties such ashigh elongation, and it is useful through a wide range of temperatures.

Rubber thread has been made by cutting narrow strips from sheet rubber,yielding thread with a square cross-section. Another method involvesstreaming uncoagulated fluid rubber ("latex" compound) through asmall-aperture nozzle or capillary into a bath of coagulant, e.g.,acetic acid, washing the coagulated thread in a water bath, and dryingand heat-curing the final product.

SUMMARY OF THE INVENTION

The invention features a rubber thread that has, in cross-section, twoor more rubber portions. One rubber portion can be, for example, thecentral core of the rubber thread, while a second rubber portion can bea jacket surrounding the central core.

A rubber thread with two rubber portions can have a mix of properties,some provided by the first rubber portion, and others by the secondrubber portion. For example, in the core/jacket embodiment, the core canbe composed of natural rubber, and thus provide the thread withexcellent resiliency, and the jacket can be composed of a sturdier,synthetic rubber that is more resistant to abrasion, fire, or chemicalattack than natural rubber. The resultant two-portion rubber thread thuswill be resistant to abrasion, fire, or chemical attack because theouter portion of the thread is composed of a rubber tailored to thatpurpose, while also having excellent resiliency because the core iscomposed of natural rubber. Similarly, a two-portion rubber thread withan outer jacket of synthetic rubber may be preferred to wholly naturalthread by customers seeking a hypoallergenic product.

The properties provided by various rubber portions can be aesthetic. Forexample, referring to the core/jacket embodiment, a rubber thread havinga particular color can be provided by including a colorant exclusivelyin the outer jacket portion of the thread. Thus, a rubber threadcomposed entirely of natural rubber can have an outer portion includingthe colorant, and an inner portion not including a colorant.Alternatively, the inner portion and outer portion can include differentcolorants, providing a rubber thread that in cross-section has twodistinct, selected colors.

The properties provided by the various rubber portions may facilitatemanufacture of the thread itself or of products made from that thread.For example, if dense chloroprene rubber is included in the outerportion to enhance fire retardancy, a lower density rubber may be usedin the core of the thread to offset the high specific gravity of thechloroprene and to prevent the thread from sinking to the bottom of thecoagulation bath. In another example, the coating may be used to adhereadjacent, touching threads into a flat tape which cannot readily beseparated back to its component threads.

The invention also features a method of making a rubber thread that hasin cross-section two rubber portions. The method includes combining afirst rubber portion and a second rubber portion. The first rubberportion and/or the second rubber portion is an uncoagulated latexcompound when the portions are combined. This provides a rubber threadthat, in cross-section, has an area composed of the first rubber portionand an area composed of the second rubber portion, that is a differentrubber than the first portion. In one preferred method, the two rubberportions (in uncoagulated form) are coextruded (either coaxially ornon-coaxially) to provide an uncoagulated rubber thread composed of twoportions. The rubber materials then are coagulated to provide thetwo-portion rubber thread.

In a second preferred method, a rubber thread including the first rubberportion is coated with the second rubber portion. The second rubberportion when coated may be uncoagulated, and after coating can becontacted with a coagulating agent. Preferably, the uncoagulated rubberincludes a sensitizer that promotes rapid coagulation of the coating,thus preventing its removal as the thread passes through the process.The invention also features a method of making a rubber thread, byconcentrically coextruding an inner stream of a first rubber portion andan outer stream of either a second rubber portion or a non-rubberportion. This results in a rubber thread in which the first rubberportion is centrally located, surrounded by the second rubber portion ornon-rubber portion.

"Rubber," as used herein, is a material that when in a solid form suchas a thread can be extehded under ambient conditions to at least twiceits resting length and, upon stress release, can return to within 15% ofits original length.

"Thread," as used herein, means a fiber of any cross-sectional shape ornumber of continuous filaments of any average diameter from about 0.200inch to about 0.0008 inch.

"Coextrusion," as used herein, means the combining of two fluid streamsinto a single fluid stream.

Other features and advantages of the invention will be apparent from thedescription of the preferred embodiments thereof, and from the claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a rubber thread having two rubberportions.

FIGS. 2 and 5 are illustrations of two methods of making rubber thread.

FIGS. 3 and 4 are perspective views of two assemblies for coextruding arubber thread having two rubber portions.

FIGS. 6-12 are cross-sectional views of rubber threads having two ormore rubber portions.

FIG. 13 is a perspective view of a rubber thread having more than onerubber portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a rubber thread 10 includes a core 12 and asurrounding jacket 14.

The core 12 preferably is composed of a natural rubber. A natural rubbercore ensures that the thread has good resiliency, particularly when thejacket 14 is not composed of natural rubber. The core preferablycomposes between 10% and 99%, and more preferably between 80% and 95%,of rubber thread 10 by weight.

The jacket 14 preferably is composed of (1) a natural or syntheticrubber that includes a colorant to provide it with a different colorthan the core 12, or (2) a synthetic rubber (with or without a colorant)that provides protection to the underlying core. The synthetic rubbermay provide abrasion resistance, oil resistance, solvent resistance,ozone resistance, UV light resistance, burn resistance, oxidationresistance, or chemical resistance generally. The synthetic rubber, forexample, may be resistant to solvents, oils, and/or metals such ascopper and manganese. Examples of preferred synthetic rubbers areacrylonitrile-butadiene (nitrile) rubbers, chloroprene rubbers, andmixtures of nitrile and chloroprene rubbers. Synthetic rubbers may alsoinclude polyurethanes, butyl, polyisoprene, and styrene-butadienerubber, or blends thereof, and the rubber may be in the form of a truesolution (in a suitable solvent), or in the form of a water-based latex.

The colorant used in the jacket may improve the appearance of the rubberthread, or provide the thread with particular cosmetic properties. Forexample, the jacket may include a whitener that provides awhiter-appearing thread, or a colorant that glows in the dark. Thecolorant also may be temperature or light sensitive, or may be selectedto provide a special effect in which the jacket has one color, and thecore, which may also contain a colorant, has a different, contrastingcolor. In another approach, all of the colorant which would normally bemixed uniformly throughout the thread may be concentrated completely inthe jacket for a more powerful effect. The jacket may include, forexample, between 0.1 percent and 30 percent colorant by weight.

Often, it will be preferable to provide a jacket that is as thin aspossible. When the jacket is composed of a synthetic rubber that hasless elasticity than the natural rubber core, providing a thick jacketpotentially may negatively affect the adhesion of the jacket orresiliency of the rubber thread. Moreover, synthetic rubber may be moreexpensive than natural rubber. In addition, when only the jacketincludes a colorant the thinner the jacket the less colorant used intotal in manufacturing the thread. Preferably, the jacket composesbetween 1% and 90%, and more preferably between 4% and 20%, of therubber thread by weight.

There are two preferred methods for making rubber thread 10.

Referring to FIG. 2, one preferred method involves flowing a coaxiallycoextruded uncoagulated rubber latex stream 16 from a glass nozzle 18into an acetic acid bath 20. The uncoagulated rubber in the streamcoagulates and hardens in the acetic acid bath. The coagulated rubberthread is rinsed in a water bath 22, and passes into an oven in whichthe rubber thread is dried in drying zone 24 and cured in curing zone26. The coagulation, rinse, dry and cure steps are performed in aconventional manner.

Coextruded rubber stream 16 is composed of a core of uncoagulatednatural or synthetic rubber latex coextruded with a jacket ofuncoagulated natural or synthetic rubber latex. The uncoagulated rubberlatex used for the core is stored in reservoir 28, and the uncoagulatednatural or synthetic rubber latex used for the jacket is stored inreservoir 30. The uncoagulated latex feeds by gravity into plastictubes, and then may be coextruded as illustrated in FIGS. 3 and 4.

The jacket may be used to adhere the adjacent, touching treads into aflat tape which cannot be readily separated back to its componentthreads.

Referring to FIG. 3, a stream of uncoagulated natural or syntheticrubber flows via plastic tubing from reservoir 30 into glass tube 32(0.156 inch ID), and at a curve flows around the exit of nozzle 34.Nozzle 34, being the end of glass tube 36 (0.058 inch ID), is connectedby plastic tubing to reservoir 28, and is positioned so that a stream ofuncoagulated natural rubber is extruded into the center of the naturalor synthetic rubber stream flowing from tube 32 to provide coextrudedrubber stream 16 in tube 38 (0.058 inch ID).

Alternatively, referring to FIG. 4, uncoagulated natural or syntheticrubber flows from external supply reservoir 30 through tube 40 (0.125inch ID) into manifold chamber 42 (0.625 inch×1.125 inch×0.250 inch).The rubber then feeds from manifold chamber 42 through a tube (0.0312inch ID×0.500 inch long) into individual chamber 44 (0.125 inch×0.125inch×0.750 inch), where the stream of uncoagulated natural or syntheticrubber flows to surround tube 46 (0.055 inch ID) as it approaches theexit of the chamber. Tube 46 connects to chamber 48 (0.250 inch×1.640inch×0.800 inch), which in turn is connected to reservoir 28 throughtube 50 (0.250 inch ID). Uncoagulated natural rubber flows fromreservoir 28 into chamber 48. It then flows through tube 46, and isextruded into the center of the uncoagulated natural or synthetic rubberstream to provide a two part rubber stream 16 (0.161 inch diameter). Thetwo rubber parts are coextruded through exit port 52 (0.055 inchdiameter), into the acetic acid bath. All components are composed ofPTFE, with the exception of tube 46, which is made of stainless steel.

The flow of the rubber streams can be controlled by adjusting the heightof the reservoirs, and by placing and adjusting thumbscrews on theplastic tubes connecting the coextrusion nozzle to the reservoirs. Thesize of the core of the final thread relative to the jacket can becontrolled, for example, by adjusting the flow rates of the respectivecore and jacket rubbers.

A 37 gauge rubber thread having a black core and a white jacket was madeusing the approach illustrated in FIG. 2. The core and the jacket hadthe following compositions:

    ______________________________________                                        Component, % wt.*    Core   Jacket                                            ______________________________________                                        Natural rubber latex**                                                                             79.46  78.37                                             Alkali solution      0.36   0.35                                              Sulfur               0.85   0.95                                              Antioxidant          1.00   0.99                                              Mercaptobenzothiazole activator                                                                    0.90   1.00                                              Fatty acid soap      0.19   0.18                                              Inert filler         4.94   0                                                 ZnO                  1.24   1.22                                              Dithiocarbamate cure accelerator                                                                   0.08   0.07                                              Black pigment        0.21   0.00                                              White pigment        0.00   5.85                                              Additional colorant  0.00   0.71                                              Water                10.77  10.26                                             ______________________________________                                         *All components are reported on an as received basis, unless indicated        otherwise.                                                                    **The latex averaged 63% total solids, achieved by blending of                conventional creamed and centrifuged rubber lattices.                    

The alkali (e.g., a 45% potassium hydroxide solution) and fatty acidsoap stabilize the latex; the sulfur provides the crosslinks to developthe desired mechanical/physical properties; the antioxidant (e.g.,Wingstay L) slows oxidative deterioration; the inert filler (e.g.,Kaolin Clay) increases the specific gravity of the black pigment; theZnO, mercaptobenzothiazole, and dithiocarbamate accelerate the cure andenhance physical properties; the black pigment provides the core withits black color; the white pigment (e.g., TiO₂) and additional colorantsprovide the jacket with its color; and the water is used to achieve thecorrect viscosity.

Referring to FIG. 5, a second preferred method of making rubber thread10 involves forming a coagulated natural rubber thread 54, whichultimately will be the core of rubber thread 10, in the conventional wayin an acetic acid bath to coagulate the natural rubber. The thread thenis washed in hot water bath 56, and then passed through dip tank 58.

Dip tank 58 includes an uncoagulated natural or synthetic rubber thatultimately will provide the jacket of rubber thread 10. Examples ofnatural rubbers that can be used include NC-358, 407, and 411, all ofwhich are available from Ennar Latex. Examples of suitable syntheticrubbers include nitriles like Perbunan N Latex VT from Bayer Corp.,Pittsburgh, PA. If a natural rubber is used, the dip material preferablyhas a pH of between 10 to 12. If a nitrile rubber is used, the dipmaterial preferably has a pH of between 9 and 11.5, and also preferablyincludes 0.2% to 3% of a sensitizer such as Basensol HA5 from BASFCorp., Charlotte, N.C., by weight. If a chloroprene rubber is used, thedip material preferably has a pH of between 9.5 and 12.0. The dip tankpreferably includes between 15% and 35% of the uncoagulated rubber byweight, and the dip material preferably has a viscosity of between 5 cpsand 40 cps.

Coated thread 54 then passes over a roller 60 that has been wetted byeither an uncoagulated rubber material, hot water, or a coagulantsolution. The coagulant solution can be used when the coating materialis natural, nitrile, or chloroprene rubber. The surface tension of thesolution preferably is under 40 dynes/cm; 28 dynes/cm is more preferred.The specific gravity (concentration) of the solution may be between 1.03and 1.16. A roller coated with hot water is preferred when the coatingmaterial is a temperature sensitive latex such as LN372C (available fromBASF). Hot water also may be used when blends of chloroprene are used asthe coating material.

The coated thread then is dipped in coagulation bath 62 to complete thecoagulation of the latex. An example of a preferred coagulant bathconsists of a calcium chloride solution (specific gravity 1.07, surfacetension 32 dyne/cm). Calcium nitrate can also be used as the coagulationagent. The thread then is washed in water bath 64, and then passes intothe standard drying/curing oven.

Alternatively, the coagulant may be applied to the uncoagulated coatingby misting or spraying.

Rubber thread 54 is pulled from the acetic acid bath at speeds ofbetween 20 feet and 60 feet per minute. A one to five percent increasein speed preferably is provided by subsequent rollers to stretch thethread.

The thickness of the coating (jacket) provided by the dip process may bebetween 0.00025 inch and 0.003 inch on a thread that has a totaldiameter of 0.035 inch. Under these circumstances, the coating isbetween 3% and 30% of the rubber thread by weight.

The dip process can also be used with rubber thread that has beenpartially or fully dried and cured in an oven. After the thread comesout of the oven, it can be sent through the dip process (wash, coat,coagulate, wash) at a speed, for example, of 60 feet per minute.

Other embodiments are within the claims. For example, the nozzle 34 inFIG. 3 and tube 46 in FIG. 4 can be positioned so that the uncoagulatednatural rubber is injected into the side of the uncoagulated natural orsynthetic rubber stream to provide a rubber thread having a stripe(where a colorant is used in the uncoagulated natural rubber), or arubber thread in which the natural rubber position is located at otheroff-center positions within the thread when examined in cross-section.In addition, in this embodiment and others, both positions of the threadcan be composed of synthetic rubbers.

Some alternative embodiments are illustrated in FIGS. 6-13. Referring toFIG. 6, a rubber thread 70 includes a core 72 and a jacket 74, arrangedin a non-concentric manner so that core 72 provides a striped surface.Referring to FIG. 7, a rubber thread 76 includes first rubber portion 78and second rubber portion 80, having a different color than portion 78.Threads 70 and 76 may be made by coextrusion techniques.

The rubber thread may include more than two rubber portions. Forexample, referring to FIG. 8, rubber thread 82 includes core 84, innerjacket 86, and outer jacket 88, arranged in a concentric manner.Referring to FIG. 9, thread 90 includes a first rubber portion 92,second rubber portion 94, and third rubber portion 96, arranged in anon-concentric manner so that portion 94 and 96 provide the thread witha striped surface. Referring to FIG. 10, rubber thread 98 includes afirst rubber portion 100, a second rubber portion 102, and a thirdrubber portion 104, each having a different color. Threads 82, 90, and98 also may be made by coextrusion.

A rubber thread having three rubber portions also may be prepared by dipcoating. For example, referring to FIG. 11, rubber thread 104 includes arubber core 106 (made in a conventional manner), an inner rubber coating108, and a rubber outer coating 110. Coatings 108 and 110 may be appliedsequentially by dip coating methods analogous to those describedpreviously.

Roll coating may be used to prepare rubber thread having two or moredistinct rubber portions. Referring to FIG. 12, rubber thread 112includes a rubber core 114, prepared by conventional methods, which canbe roll-coated to provide a rubber portion 116 covering part of thesurface of core 114. Portion 116 may have a color different from core114 to provide a striped thread.

The rubber thread also may have a core and jacket portion that vary inthickness. For example, referring to FIG. 13, a rubber thread 118includes a core 120 and a jacket 122 that varies regularly in thicknessalong the entire axial length of the thread. Jacket 122 reduces inthickness to essentially zero at intermittent points along the core; ifjacket 122 has a different color than core 120, the thread is providedwith circumferential stripes 124 along its exterior.

We claim:
 1. A rubber thread comprising, in cross-section, a firstrubber portion comprising a natural rubber and a second rubber portioncomprising a synthetic rubber.
 2. The rubber thread of claim 1, whereinsaid first portion is centrally-located in said rubber thread, and saidsecond rubber portion surrounds said first rubber portion.
 3. The rubberthread of claim 2, wherein said second rubber portion includes acolorant that provides it with a color that is different than the colorof said first rubber portion.
 4. The rubber thread of claim 2, whereinsaid second rubber portion is more resistant to abrasion than said firstrubber portion.
 5. The rubber thread of claim 2, wherein said secondrubber portion is more resistant to ultraviolet light than said firstrubber portion.
 6. The rubber thread of claim 2, wherein saidsecond-rubber portion is more resistant to solvents or other chemicalsthan said first rubber portion.
 7. The rubber thread of claim 2, whereinsaid second rubber portion is more resistant to fire than said firstrubber portion.
 8. The rubber thread of claim 2, wherein said secondrubber portion is less likely to provide an allergic response than saidfirst rubber portion.
 9. The rubber thread of claim 2, wherein saidsecond rubber portion comprises between 2% and 80% of said rubber threadby weight.
 10. The rubber thread of claim 2, wherein said second rubberportion comprises a nitrile rubber.
 11. The rubber thread of claim 2,wherein said second rubber portion comprises a chloroprene rubber. 12.The rubber thread of claim 2, wherein said second rubber portioncomprises a butyl rubber.
 13. The rubber thread of claim 12, whereinsaid first rubber portion includes a colorant that provides it with adifferent color than said second rubber portion.
 14. The rubber threadof claim 2, wherein said second rubber portion comprises a polyurethanerubber.
 15. The rubber thread of claim 2, wherein said second rubberportion comprises a styrene-butadiene rubber.
 16. The rubber thread ofclaim 2, wherein said second rubber thread comprises a syntheticpolyisoprene rubber.
 17. The rubber thread of claim 2, wherein saidsecond rubber portion comprises a rubber selected from the groupconsisting of nitrile rubber, chloroprene rubber, butyl rubber,polyurethane rubber, styrene-butadiene rubber, natural rubber, syntheticpolyisoprene rubber, or a blend including two or more of the foregoingrubbers.
 18. The rubber thread of claim 1, further comprising, incross-section, a third rubber portion in addition to said first rubberportion and said second rubber portion.
 19. A rubber thread comprising,in cross-section, a first rubber portion surrounded by a second rubberportion having a composition different from said first rubber portion.20. The rubber thread of claim 19, wherein said first rubber portioncomprises a natural rubber and said second rubber portion comprises asynthetic rubber.
 21. The rubber thread of claim 20, wherein saidsynthetic rubber is a nitrile rubber.
 22. The rubber thread of claim 20,wherein said synthetic rubber is a chloroprene rubber.
 23. The rubberthread of claim 20, wherein said first portion is centrally-located insaid rubber thread.
 24. The rubber thread of claim 19, wherein saidsecond rubber portion includes a colorant that provides it with a colorthat is different than the color of said first rubber portion.
 25. Therubber thread of claim 19, wherein said second rubber portion is moreresistant to abrasion than said first rubber portion.
 26. The rubberthread of claim 19, wherein said second rubber portion is more resistantto ultraviolet light than said first rubber portion.
 27. The rubberthread of claim 19, wherein said second rubber portion is more resistantto solvents or other chemicals than said first rubber portion.
 28. Therubber thread of claim 19, wherein said second rubber portion is moreresistant to fire than said first rubber portion.
 29. The rubber threadof claim 19, wherein said second rubber portion is less likely toprovide an allergic response than said first rubber portion.
 30. Therubber thread of claim 19, wherein said second rubber portion comprisesbetween 2% and 80% of said rubber thread by weight.
 31. The rubberthread of claim 19, wherein said second rubber portion comprises a butylrubber.
 32. The rubber thread of claim 19, wherein said second rubberportion comprises a polyurethane rubber.
 33. The rubber thread of claim19, wherein said second rubber portion comprises a styrene-butadienerubber.
 34. The rubber thread of claim 19, wherein said second rubberthread comprises a synthetic polyisoprene rubber.
 35. The rubber threadof claim 19, wherein said second rubber portion comprises a rubberselected from the group consisting of nitrile rubber, chloroprenerubber, butyl rubber, polyurethane rubber, styrene-butadiene rubber,natural rubber, synthetic polyisoprene rubber, or a blend including twoor more of the foregoing rubbers.
 36. The rubber thread of claim 19,further comprising, in cross-section, a third rubber portion in additionto said first rubber portion and said second rubber portion.
 37. Therubber thread of claim 19, wherein the rubber thread is substantiallycircular or elliptical in shape.
 38. A rubber thread comprising, incross-section, a first rubber portion and a second rubber portion havinga different composition than said first rubber portion and being anuncoagulated latex compound.